Light trapping photonic crystal (PhC) patterns on the surface of Si solar cells provides a novel opportunity to approach the theoretical efficiency limit of 32.3%, for light-to-electrical power conversion with a single junction cell. This is beyond the efficiency limit implied by the Lambertian limit of ray trapping ~ 29%. The interference and slow light effects are harnessed for collecting light even at the long wavelengths near the Si band-gap. We compare two different methods for surface patterning, that can be extended to large area surface patterning: 1) laser direct write and 2) step-&-repeat 5 × reduction projection lithography. Large area throughput limitations of these methods are compared with the established electron beam lithography (EBL) route, which is conventionally utilised but much slower than the presented methods. Spectral characterisation of the PhC light trapping is compared for samples fabricated by different methods. Reflectance of Si etched via laser patterned mask was ~ 7% at visible wavelengths and was comparable with Si patterned via EBL made mask. The later pattern showed a stronger absorbance than the Lambertian limit 6 .

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Capabilities of the attenuated total reflection (ATR) at THz wavelengths for increased sub-surface depth characterisation of (bio-)materials are presented. The penetration depth of a THz evanescent wave in biological samples is dependent on the wavelength and temperature and can reach 0.1–0.5 mm depth, due to the strong refractive index change ∼0.4 of the ice-water transition; this is quite significant and important when studying biological samples. Technical challenges are discussed when using ATR for uneven, heterogeneous, high refractive index samples with the possibility of frustrated total internal reflection (a breakdown of the ATR reflection mode into transmission mode). Local field enhancements at the interface are discussed with numerical/analytical examples. Maxwell’s scaling is used to model the behaviour of absorber–scatterer inside the materials at the interface with the ATR prism for realistic complex refractive indices of bio-materials. The modality of ATR with a polarisation analysis is proposed, and its principle is illustrated, opening an invitation for its experimental validation. The sensitivity of the polarised ATR mode to the refractive index between the sample and ATR prism is numerically modelled and experimentally verified for background (air) spectra. The design principles of polarisation active optical elements and spectral filters are outlined. The results and proposed concepts are based on experimental conditions at the THz beamline of the Australian Synchrotron.

Orientational dependence of the IR absorbing amide bands of silk is demonstrated from two orthogonal longitudinal and transverse microtome slices with a thickness of only ∼100 nm. Scanning near-field optical microscopy (SNOM) which preferentially probes orientation perpendicular to the sample’s surface was used. Spatial resolution of the silk–epoxy boundary was ∼100 nm resolution, while the spectra were collected by a ∼10 nm tip. Ratio of the absorbance of the amide-II C-N at 1512 cm − 1 and amide-I C=O β -sheets at 1628 cm − 1 showed sensitivity of SNOM to the molecular orientation. SNOM characterisation is complimentary to the far-field absorbance which is sensitive to the in-plane polarisation. Volumes with cross sections smaller than 100 nm can be characterised for molecular orientation. A method of absorbance measurements at four angles of the slice cut orientation, which is equivalent to the four polarisation angles absorbance measurement, is proposed.